Syntactic foams are composite materials in which hollow particles, such as microspheres are dispersed in a resin matrix. It is known in the prior art that syntactic foams can be prepared whose composition is such that they cannot be dissolved in water or low-molecular weight alcohols. For example, U.S. Pat. No. 5,120,769 (Dyksterhouse et al.) discloses a foam which incorporates water as a non-solvent and whose thermoplastic component is not readily soluble in water or low-molecular weight alcohols. Also known in the prior art is the preparation of syntactic foam composed of carbon microspheres in a carbon matrix, as disclosed in U.S. Pat. No. 3,832,426 (Malthouse et al.), which foam would not be soluble in water or low-molecular weight alcohols.